(1) Field of the Invention
This invention relates to polymer composites. More particularly, this invention relates to a technique for grafting organic materials as such, with isocyanate and may be mixed with an inorganic material bonded or not with a bonding agent. Bonding the isocyanated material with a thermoplastic resin produces either composites having improved physicomechanical properties, or composites having only strongly bonded components.
So, this invention is a continuation-in-part of Beshay's U.S. Pat. Nos. 4,717,742 and 4,820,749.
(2) Description of Prior Art
The modification of the physical and mechanical properties of thermoplastic, thermosetting or rubbers by the addition of a filler is well known in the art. Greater degrees of property improvement result when the filler is uniformly and highly dispersed throughout the polymer matrix and/or when its chemical interface provides a possible site weakness in the composite.
Various means for improving the compatibility of the filler with the polymer matrix by providing an interaction between the filler and the polymer are known in the art. For Example, when a cellulosic material, such as wood fibers, or cotton fibers, are used as a filler in the polymers containing methylol groups such as phenolic urea or melamine resins, a reaction occurs between the methylol groups and the hydroxyl groups on the cellulosic filler. Inorganic fillers such as calcium carbonate, clay or asbestos have been encapsulated and dispersed in a polyolefin in order to obtain improved properties. Some materials such as maleic anhydride or others were bonded by the effect of the initiating agents such as peroxides. In such a system, the polymer used to coat the filler should be chemically bonded to the filler in order to obtain optimum properties such as high strength.
The published literatures include a number of proposals, which consist essentially of thermoplastic resinous matrix having dispersed therein cellulosic fillers mixed or not with inorganic fillers. Such materials are described for example:
U.S. Pat. No. 3,485,777 (1969), Gaylord, deals with compatibilization of polyvinylchloride or polymethylmethacrylate with grafted cellulose.
U.S. Pat. No. 3,645,939, also shows that polyethylene or polyvinyl chloride or acrylic rubber can be compatibilized with cellulosic fibers in presence of an ethylenically unsaturated carboxylic acid or anhydride under conditions which generate free radical on said polymer and cellulose.
U.K. Pat. Appl. No. 2090849, Hishida, I., prepared composites from thermoplastic resins by compatibilizing flax fibers coated with a surface treating agent such as silanes, titanates, . . . etc. in absence of a free radical initiator.
U.S. Pat. No. 4,554,215, Robbart, made composites coated with alkylhalogeno-silane, also in absence of an initiator.
U.S. Pat. No. 4,374,178, Kulkarni, prepared composites by filling with calcium carbonate or sodium silicate and a microcrystalline cellulose as a carrier by coating with silane bonding agent.
E.P. Pat. No. 0008143, Solvay & Cie and the Japanese Pat. No. 8011-537, Showa, both teach the application of organic and inorganic fillers in presence of a peroxide and an acid anhydride; resulting composite materials having relatively little improvements in their mechanical strengths.
J 5 Pat. No. 7192-466, Showa, teaches the addition of an unsaturated silane coupling agent onto the polyolefin matrix by the effect of a catalytic peroxide and then by adding wood flour as a filler, but by silylating the matrix leads to consuming more silane than in case of silylating the filler itself. Furthermore, the composite performances are not highly improved.
U.K. Pat. Appl. No. 8705045, prepared composites with just coating the wood pulps with isocyanate bonding agents by assuming the formation of interfacial covalent bonding and in absence of any specific catalyst leading to the grafting of isocyanates onto the cellulosic fibers. Furthermore, no inorganic filler pretreated with any bonding agent was added to mix with the organic filler.
The applicant, in his Ca. Pat. No. 1252586 and the U.K. Pat. Appl. No. 2205569, Beshay, realized more improvements by mixing the silane grafted cellulosic fibers with a silane bonded inorganic fillers.
According to the present invention, the isocyanate grafting and bonding process creates strong attachments between the mixture of components and the isocyanate agent. The grafting process could either be partial or complete. The process could be completed by the effect of a hot molten polymer resin, which provides sites for the formation of free radicals with desired degrees of loading by the initiation effect to attach by chemical bonding to the other side of the isocyanate molecules, which are pregrafted and prebonded with the mixture of materials. Thus for example, the properties of polyethylene, polystyrene and polyvinylchloride are improved by the incorporation of the grafted filler mixture in the presence of a free radical catalyst such as dicumyl peroxide. The composition ratios range from 1 to 99% by weight of the grafted and bonded isocyanated materials.
In summary, we believe to be the first to prepare composites of polymeric resin or resin blend and cellulosic fibers grafted with isocyanates by generating a free radical process and which may mix with inorganic filler(s), prebonded or not, with a bonding agent; if the cellulosic fibers are coated with isocyanates, it is provided to mix with bonded inorganic filler(s) with bonding agent(s).